1. Field of the Invention
The present invention relates to an air conditioner having an indoor heat exchanger and an outdoor heat exchanger of a small-sized type without decreasing the performance or ability of the air conditioner.
2. Description of the Prior Art
In general, an indoor unit in an air conditioner has an indoor heat exchanger and an outdoor unit in it has an outdoor heat exchanger.
As shown in FIG. 1A, the heat exchanger comprises a plurality of fins 101 and a heat exchanger tube 103 which is located through the plurality of fins 101. In this case, the heat exchanger tube 103 has a one path configuration.
Now, we explain about the number of paths of the heat exchanger tube. As shown in FIG. 1A, a heat exchanger tube 103 of a one path type from the inlet side to the outlet side is referred to as "a one path type". As shown in FIG. 1B, a heat exchanger tube 103 is branched into two paths at the inlet side of it and the branched two paths are grouped to a one heat exchanger tube at the outlet side of it. This type configuration is called as "a two path type". In addition, as shown in FIG. 1C, a heat exchanger tube 103 has a one path at the inlet side and it is branched into two path at a mid-point and the two path is grouped to a one path at the outlet side of it. This type configuration is referred to as "1-2 path type". As shown in FIG. 1D, a heat exchanger tube 103 is branched into two paths at the inlet side and the two paths are further branched into three paths at the outlet side of it. This type configuration is referred to as a "2-3 path type". Thus, there are various path types based on a combination of the number of branches in a heat exchanger tube. These type configurations of the heat exchanger tube are examples.
In a heat exchanger, a heat exchanging operation is performed between a coolant flowing in the heat exchanger tube 103 and an air flowing between the fins 101. Important factors in order to change the ability of a coolant are a pressure loss .DELTA. P and a heat transfer coefficient .alpha.. As you know, when the pressure loss .DELTA. P becomes smaller and the heat transfer coefficient .alpha. is greater, the efficiency of the heat exchanging operation in the heat exchanger becomes high.
By the way, the heat transfer coefficient .alpha. is expressed by a relationship between the Nusselt number and the Reynolds number. Thus, we can obtain the following relationship expression: EQU .alpha..multidot.D/.lambda.=C1.multidot.((M/A).multidot.D/.mu.).sup.c2,
where M is a circulating amount of a coolant, .lambda. is a heat transfer coefficient, .mu. is a viscosity coefficient, D is a diameter of a heat exchanger tube, A is a cross section area, and C2 is a constant.
When C2.apprxeq.1 and N is the number of paths, we obtain the following relationship: EQU .alpha..varies.M.multidot.(.lambda./.mu.)/(D2.multidot.N) (1)
On the other hand, the pressure loss .DELTA. P is a function of a dynamical pressure. Therefore we obtain the following relationship: EQU .DELTA.P=C3.multidot.(Lm/D).multidot..rho..multidot.(M/(.rho..multidot.A)). sup.2,
where M is a circulating amount, D is a diameter of a heat exchanger tube, A is the cross section area, .rho. is a density of a coolant, and Lm is a length of a flow path.
When Lm=L/N, L is the total length of the heat exchanger tube, the following relationship is obtained: EQU .DELTA.P.varies.M.multidot.(1/.rho.).multidot.L/(D.sup.5 .multidot.N.sup.3)(2).
These equations (1) and (2) described above show apparently that the heat transfer coefficient .alpha. becomes greater, but the pressure loss .DELTA. P also becomes greater when the diameter D of the heat exchanger tube is shorter and the number of the paths is smaller.
We define a total performance index or a combined performance lndex for evaluating the combined performance of a heat exchanger as follows: EQU I=(.DELTA.P/ P)/.alpha. (3),
where P is an average pressure in the heat exchanger and (.DELTA. P/P) is a value for directly expressing that the pressure loss .DELTA. P has an effect on the cycle efficiency of an air conditioner.
Accordingly, when the equations (1) and (2) are introduced into the equation (3), we obtain the following relationship as the circulating amount of the coolant by a displacement of M=m.multidot.H, EQU I.varies.(.mu./(.rho..multidot..lambda..multidot.P)).multidot.m.multidot.(H .multidot.L/(D.sup.3 .multidot.N.sup.2) (4),
where m is a circulating amount of a coolant per unit output, and H is a rated output (kw) of an cooling operation.
As apparently by the equation (4) above, in order to decrease the combined performance I as small as possible, namely in order to increase the total performance of the heat exchanger, the diameter of the heat exchanger tube must be larger and the number of paths is also increased. This is easily understood based on the equation (4) above. However, when the diameter of a heat exchanger tube is larger, the size of a heat exchanger becomes greater. In addition, the number of paths is increased, a coolant cannot flow into each path uniformly. For example, a flow amount of a coolant stream into each path is a slightly different to each other. Accordingly, an designer must decrease the diameter D of a heat exchanger tube and the number N of paths during design of an air conditioner. These are important objects of the designer.
For example, in a conventional small-size indoor air conditioner using fluorocarbon-based coolant R22 as a coolant, it is generally used that the total length of a heat exchanger tube is approximately 20 meters, an outer diameter of the heat exchanger tube is approximately 35 mm, and the heat exchanger tube is a two paths type configuration. It is quite rare that a part of a heat exchanger tube is a one path type or three path type. In addition, in an outdoor heat exchanger, it is generally used that the total length of a heat exchanger tube is about 20 meters, an outer diameter of the heat exchanger tube is approximately 8 mm, and the heat exchanger tube is the two paths type configuration. It is quite rare case in an outdoor heat exchanger configuration that the diameter of the heat exchanger tube is 8 mm or 9.52 mm.
Now, in the equation (4) described above, namely in the following equation (4): EQU I.varies.(.mu./(.rho..multidot..lambda..multidot.P)).multidot.m.multidot.(H .multidot.L/(D.sup.3 .multidot.N.sup.2) (4),
when .kappa. is used for the component [H.multidot.L/(D.sup.3 .multidot.N.sup.2)], we obtain the results in the following TABLE-1 which are calculated by using actual data items for each of heat exchanger of conventional various types.
TABLE-1 ______________________________________ Rated Type of heat output exchanger [kw] L [mm] D [mm] N .kappa. ______________________________________ indoor small sized 2.8 20,000 6.35 2-3 39.5 indoor small sized 2.8 20,000 6.35 2 54.6 indoor small sized 2.8 20,000 6.35 1-2 103.9 indoor large sized 7 40,000 6.35 3 91.8 indoor large sized 14 60,000 8 5 65.5 outdoor small sized 2.8 20,000 9.52 2 16.2 outdoor small sized 2.8 20,000 8 2 27.4 outdoor small sized 2.8 20,000 7 2 40.6 outdoor large sized 5 40,000 9.52 3 25.8 outdoor large sized 14 100,000 9.52 6 45.1 ______________________________________
For example, when the entire of a heat exchanger tube in a small sized indoor heat exchanger is constructed by a one path configuration, .kappa. becomes 218.7 which is greater than that in each case of the heat exchangers in the table 1. In this case, the performance of this small sized heat exchanger become down or decreased. This is a problem.